attribute.rst

Attribute

Sidre Attribute objects enable users to attach metadata (strings and values) to Sidre views to support queries (e.g., search for views with a given attribute name), outputting data for a subset of views to files, and other ways an application may need to selectively process views in a Sidre data hierarchy.

An attribute is created with a string name and a default scalar or string value. A default value can be changed later as needed.

Note

• Attribute objects can only be created and destroyed using DataStore class methods. The Attribute class constructor and destructor are private (see :ref:`datastore-label`).
• Each Attribute object has a unique name and integer identifier. Either can be used to retrieve an Attribute object from a DataStore object..

Each Sidre view inherits all attributes contained in a datastore with their default strings or values. Then, an application may explicitly set any attribute on a view. The application may also query the value of a view attribute, query whether the attribute was explicitly set, or set the attribute back to its default value. See :ref:`view-label` for more information about View objects.

The Attribute class provides the following operations:

• Retrieve the name and unique id of an attribute
• Set the scalar or string value of an attribute
• Get the type of an attribute's scalar value

One can iterate through the attributes in the datastore using either "range-for" or iterator syntax:

// 'range-for' syntax
for(auto& attr: datastore->attributes()) { /* ... */ }

// 'iterator' syntax:
for(auto it = datastore->attributes().begin(),
      itEnd = datastore->attributes().end(); it != itEnd; ++it)
{
  auto& attr = *it;
  /* ... */
}